Effects of BPS, 8-Br-cAMP, hypoxia, and PDGF on p27kip1protein stability. Cultured HPASMC were exposed to 21% or 2% oxygen with or without 10 μM BPS, 1 mM 8-Br-cAMP, or 25 ng/ml PDGF and 25 μg/ml of CHX for indicated periods and Western blotted. Degradation of p27kip1 expression did not significantly change among cells exposed to hypoxia, BPS, or 8-Br-cAMP. PDGF promoted degradation of p27kip1 protein expression. Graphs show % of maximal p27kip1 protein expression. Line with solid circles, 21% oxygen (control); dotted line with open circles, 2% oxygen (hypoxia); line with solid squares, PDGF; dotted line with open triangles, BPS; dotted line with solid triangles, 8-Br-cAMP. Data are expressed as means ± SE (n = 4). *P < 0.05 versus 21% oxygen.